Card – picture – or sign exhibiting – Photographic transparency viewer – e.g. – x-ray viewer
Utility Patent
1998-02-23
2001-01-02
Davis, Cassandra H. (Department: 3633)
Card, picture, or sign exhibiting
Photographic transparency viewer, e.g., x-ray viewer
C040S361000, C353S038000
Utility Patent
active
06167646
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention disclosed and claimed herein generally pertains to improved view box apparatus, of the type used to illuminate a film containing a radiographic or other medical diagnostic image for viewing and study. More particularly, the invention pertains to apparatus of such type wherein the contrast and resolution, or sharpness, of a viewed image is significantly improved or enhanced, whereby viewability is improved.
As is well known, a view box, also known as a light box, is a device used by radiologists to view and study radiographic images and other medical diagnostic images which are on film. Such images, showing selected views of body tissue, can be obtained by means of conventional X-ray, computed tomography (CT), magnetic resonance imaging (MRI), and other techniques known to those of skill in the medical diagnostic imaging arts. By carefully studying such images, a radiologist can note the presence of significant medical conditions in a patient or other subject, without the need for invasive surgery. Some important examples of such conditions include breast cancer, lung cancer, pneumonia, fracture, and arthritis.
A conventional view box generally contains one or more fluorescent tubes or other sources of light, and has a front panel typically comprising a translucent light diffuser, such as a sheet of milky white plexiglass. The radiographic imaging film is placed on the light diffuser and transilluminated, for viewing and study, by light from the light source. The light passes through the diffuser and is diffused or scattered thereby. Thus, the light transmitted to the imaging film is of uniform brightness or intensity, so that the imaging film is uniformly illuminated.
If a view box was not provided with a diffuser or other means for scattering light from the fluorescent tube light source, the fluorescent tubes would tend to be seen through the imaging film, interfering with the study thereof. However, the scattering or diffusing of illuminating light causes contrast between lighter and darker regions on the imaging film, as well as resolution, to be degraded from the perspective of an observer. More particularly, because the light which carries the film image to a viewer's eye is diffused, edges or boundaries between lighter and darker regions of the image are blurred, as received on the retina of the viewer. Thus, the radiologist's task of correctly interpreting a film image is made more difficult. Certain conditions, such as breast cancer, lung nodules, and small pneumothorax (collapsed lung) are especially hard to detect in any event. If there is too much blurring of edges, or insufficient contrast between lighter and darker areas of a film image, a correct diagnosis of such conditions may not even be possible. The term “resolution,” as used herein, means the level of sharpness or blurring which characterizes the boundary, or edge, between adjacent lighter and darker regions of an image.
The importance of providing a high level of contrast and resolution, in illuminating a diagnostic imaging film, is further emphasized by certain regulations of the U.S. government. Under federal law, all X-ray equipment used in the United States for mammography, that is, for acquiring radiographic images for detecting breast cancer, must be periodically tested for contrast and resolution. Such test is conducted by producing a radiographic image of a standardized mammography phantom, which is analyzed by a federal inspector or medical personnel. If the inspector determines that contrast or resolution of the image is insufficient, the facility at which tile equipment is located will not be allowed to perform further mammography until the situation is corrected. Such federal standards have been put into place because, if there is insufficient contrast between two adjacent areas of slightly different density in a breast, or insufficient resolution along the edge therebetween, a subtle breast cancer (characterized by an only slightly different density from surrounding normal breast tissue) will not be detectable. This, in turn, may result in a delay of treatment, which could cause great harm to a patient.
In the past, it has been suggested that contrast of a medical diagnostic imaging film, illuminated by means of a view box, could be improved by substantially increasing the spatial separation between the light source and the imaging film. Thus, the light illuminating the film would become less diffused i.e., the solid angle thereof, as described hereinafter in further detail, would decrease. However, the proposed spatial separation was on the order of six to twelve feet, whereas the depth of a conventional view box is generally less than one foot. It would be highly impractical for a number of reasons, including cost and spatial constraints, to construct a view box having the proposed expanded dimensions.
The inventor herein is not aware of any prior art relating decrease in diffusion of illuminating light to improvement in resolution.
SUMMARY OF THE INVENTION
The invention provides apparatus for illuminating a medical diagnostic imaging film, and includes means for supporting the imaging film in a specified plane. The invention further comprises means for projecting light toward the supported imaging film, the projected light having a first solid angle. A light directing film means is positioned between the imaging film and the light projecting means so that the projected light is incident on the light directing film means. The light directing film means selectively reflects and/or refracts at least a portion of the projected light to provide redirected light for illuminating the imaging film, the illuminating light having a second solid angle which is substantially less than the first solid angle. Preferably the light directing film means comprises one or more layers of a film having a number of microscopic prism elements, or microprisms, formed on one side.
The term “solid angle,” as used herein is a measure of the divergence, diffusion, or scattering of a quantity of light, such as light projected toward, or illuminating the plane of the imaging film. The solid angle is oriented along an axis which is orthogonal to the film plane, and may vary from zero degrees, i.e., parallel light, to on the order of 180 degrees, i.e., very scattered or diffused light.
In a preferred embodiment, the light directing film means has an associated critical angle and is in parallel relationship with the specified plane. Some of the rays of the projected light, respectively directed along lines intersecting the specified plane at angles which are less than the critical angle, comprise a first portion of projected light. Other of said projected light rays, respectively directed along lines intersecting the specified plane at angles which are greater than the specified critical angle, comprise a second portion of projected light. The light directing film means prevents transmission of the first projected light portion to the imaging film, and refracts the second projected light portion, so that respective rays thereof are converged to lie within the second solid angle.
OBJECTS OF THE INVENTION
An object of the invention is to improve or enhance contrast and resolution provided by apparatus illuminating radiographic and other medical diagnostic imaging films for viewing.
Another object is to provide view box apparatus for diagnostic imaging film, wherein contrast and resolution are enhanced without significantly increasing cost or complexity over prior art view boxes.
Another object is to provide view box apparatus of the above type which substantially retains the dimensions of currently used view boxes.
Another object is to provide a view box of the above type which may be readily constructed by retrofitting, with comparative simplicity, a prior art view box.
These and other objects of the invention will become more readily apparent from the ensuing specification, taken together with the accompanying drawings.
REFERENCES:
patent: 5594830 (1997-01-01), Winston
Davis Cassandra H.
Skarsten Law Offices S.C.
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